Many items of manufacture are sold based on function as well as looks. These items are often provided with a protective or ornamental coating which can wear off with extended use. For example, the alphanumeric and special function keys on a cell phone, computer keyboard, radio, television, TV remote, game console, appliances and the like, are used repeatedly. Membrane switches and keypads and silicon rubber keypads are commonly present on such devices. The switches and keys are subject to repeated actuations, typically by a human finger. Oils and salts in human skin helps to break down or wear away identifying symbols made from paints, inks or coatings on the surface of keys or switches. Keys and switches are also subject to other conditions which cause wear to the exposed surfaces such as wiping, cleaning, and rubbing during normal use, handling, shipping, and storage.
After repeated use, the symbols or graphics on the appliance keys wear away to the point that symbols are unattractive or totally illegible, possibly rendering the items unusable. For example, it is important to determine the resistance to wear of buttons or number pads of items such as video or tv remotes which may wear off after continued use. The infrequent user who is not as familiar the function of all the keys can become very frustrated when trying to use such a device with often used keys which are now unlabeled.
Manufacturers employ tests of various types such ensure quality and reliability of alphanumeric and symbolic labels on keys and switches. Examples of such tests include a test wherein a sharp pinpoint is used to scratch a surface of a test sample. The amount of damage is measured and compared to other tested samples. Another type of test uses a spinning ball which is moistened with a polishing slurry which is urged against the test surface for a selected amount of time. The resulting amount of wear is measured and compared to other test samples.
Examples of surfaces types to be tested include items with coatings such as paints, acrylics and the like, items with applied or adhesive layers such as plastics and mylars, and injection molded items wherein alphanumeric symbols are molded within the key in a process called double shot injection molding. Due to the use of extremely thin overlays and new types of coatings which contain the symbols which are applied to the surface of keys or other surfaces on appliances, toys, computers, and so forth, the quality, reliability and durability of these applied symbols is critical.